IVR - interactive voice response
every phone system has its own methods of implementing an IVR to work with the system... and now, there are many VoIP providers that cater to businesses that host the IVR or "phone system features" on there server - which is off site of the customers location.
most IVR systems use a touch tone response system, where you key in your choices with the dial pad of the phone, but some of the newer systems use voice recognition to allow you to speak your answers...